20 Admonitions(Niju kun)
  The teachings of  Dai sensei Funakoshi Gichin were always filled with philosophical meaning. His twenty admonitions to students of karate are universal in their wisdom and the application of karate-do not only in the Karate dojo but also in daily life

Don't forget that Karate begins and ends with etiquette and courtesy.

  The Emphasis on courtesy is not just for the sake of learning proper behavior but also to build humility and respect for other beings.
Karate should only be used when one is attacked first.
  Karate-do is the art of empty handed self defense. This defensive aspect of the art is emphasized  repeatedly to a student of karate so that the art is never misused . The extent to which the great masters laid emphasis on this is can be seen in the Shotokan Karate-do Kata, where the first movement is always a block.
The trait of righteousness is what makes karate the art that it is.
  To stand up for truth and uphold all that is right and truthful makes the Karateka unafraid in the face of danger This can also be seen in the Dojo Kun.
Firstly know yourself and only after that can you know another.
  Man is always critical of others or has opinions about others. This advise is another example of the emphasis the Master laid on humility when he expounds that unless you know yourself, your own weaknesses, your desires, your fears etc.,and your own strength, it is difficult to fight someone else about whose nature you know nothing at all.
The right mental aspect  is as important  as the physical aspect of the technique.
  To carry out a technique one needs to be able to do it physically, in order to do it correctly, one must understand it completely but to execute it completely one must have the right attitude. Therefore the emphasis on training should not solely be on the physical aspect but the karateka should also build up the right mental attitude.
It is necessary to detach your mind when practicing.
  The mind is amongst the most difficult things to control. The practice of karate inculcates self discipline which demands a control over the mind. This is because complete undivided attention is needed when practicing Karate. If one's mind is occupied with matters other than that being done at any given moment, then completely mastery whether physical or mental over what is being taught at that point of time cannot be achieved. Therefore a cold mindset completely detached from everything else except what is being done or taught is necessary.
Laziness makes ruin.
  No explanations are necessary for this since the practice of Karate-do directly involves the eschewing of laziness.
Don't think that karate is only in the dojo.
  The term Karate-do means the way of Karate. It is necessary for those who walk this path to know that the way of karate cannot be restricted only to the confines of the dojo. It is the manner in which one conducts one's self not only in the dojo but also outside of it in the day to day activities of life.
Karate training is throughout life.
  It is necessary for those who practice the way of karate to know that training is not to be restricted only to the period of the dojo practice but that the essence of the art is that it can be trained throughout one's life. Unlike many other forms of physical training, karate -do can be used to stay healthy both physically and mentally. The self discipline inculcated thus also helps one spiritually throughout one's life.
If you Karate-ize everything then there is exquisiteness.
  Funakoshi Dai-Sensei used Zen philosophy to propagate the essence of karate-do. This admonition to those who practice karate is again his manner of stating that when you use the philosophy of karate-do in everything you do, then everything that you do can be seen in a different perspective.
Karate is just like hot water if you do not give it heat it will become cold water.
  One of the most commonly used adages in the JKA Karate-do, this simple but very effective line states in a direct manner the need for training everyday and why it is most necessary to do so, if you want to keep your standard high.
You need not think of winning but it is necessary to think of not losing either.
  Very sound advice to a martial artist often given to competitors by their coaches. Dai Sensei Funakoshi in a single sentence metes out this advice of the need to be totally aware of the present.  By thinking of winning , one's mind is occupied by this aspect rather than being completely aware of the present. Similarly, if at any point of time things do not seem to be going well for  oneself, it is very important that one does not think of losing either. What is needed therefore is to only concentrate on executing the technique as per the strategy thought out to the best of one's ability.
You must change your attitude and technique according to the enemy.
  Again a simple but straightforward explanation that every person is different and that every situation begets a different reaction. There always is a case by case answer to any situation and one needs to adapt oneself accordingly.
Fighting is dependant on the control of truth and feinting or faking.
  Strategy is the use of half truths and the presentation of what seems to be the truth but in reality far from it. Masking one's intentions till the last minute is true control of strategy and mastery of this is necessary for the winning of any situation in one 's favor.
You must think of a person's hands and feet as swords.
  Karate-do started out as a purely art of self defense at a time where the average native of Okinawa was banned from using or carrying weapons and this being the case, in the ancient days to parry a sword cut, one had to make one's hands and feet  weapons that could be equal stature and strength. In  modern times though the situation is completely different, karate-do being a martial art, one's hands and feet are one's weapons therefore the necessity to train accordingly.
Once a man comes out of a gate there are a million enemies.
  Never rest because every moment of  life is always a challenge seems to be the message that is given by this advice. Once one has taken a step forward, one must move ahead fighting keeping the spirit up.
Kamae (Pose) is for beginners later it is natural instinctiveness.
  The concept of the relation between muscle memory and instinct was not scientifically proven when Dai Sensei Fuankoshi wrote the Niju kun. However one can interpret his advice in this light. Repeatedly training correctly in the basics as a beginner makes these techniques to become a second nature moving them to the realm of the instinct. Therefore instinctive reaction can be based on karate.
Kata should be correct, Jissen (actual combat) is different.
  The term kata means "formal way". The oyu of the bunkai of  kata is however based on Jissen or actual combat. Therefore do the kata in the right manner, with the knowledge that Jissen is different.
Don't forget the basic principle - Expansion and Contraction of the body, The Correct use of power, and Speed during movement.
  Dai Sensei Funakoshi stressed on the 3 principles of kata.- 1) the Expansion and contraction of the body. - in large and small movements 2) The correct usage of power. In movements where strength if required use strength, in the movement that one has to relax, and not use strength, such should be the case 3) the usage of speed and slowness of movement in movements where acceleration or deceleration is required.
You must plan and devise strategy.
  Always have foresight in everything you do. Plan well and think strategically, have backup plans incase the ones devised do not work.

The matter in bold has been translated from Japanese and therefore may seem grammatically incorrect in English. The explainations are those given by Sensei Anand Ratna .