One of the bad points of being an INTP is not being able to see things through as well as other types, but that downfall is greatly compensated by many benefits this type has. For example when an INTJ is theorizing they will make theories which translate over to an actuall plan or system, while an INTP gets to make much broader theories which are not limited by the need to be applied, so are much more creative.
Because of how this thread has progressed I think here is a good time to settle something with you fellow intpforumers.
Here it is: P means Perceiving and J means Judging, in regard to MBTI types the point of these last 2 possible letters is to point to the primary function of the type , rather than be used like the other letters. That may of been confusing so first look at this.
Your type breaks up into four letters, the first letter is obvious, whether your introverted or extraverted, the second letter is the two perceiving functions: Sensing and iNtuition, the third letter is the two Judging functions: Thinking and Feeling and the final letter is used to find your primary function, so distinguish whether your primary function is a primarily judging or a perceiving.
If your type is ENTJ your primary 2 letter type is found by first looking at the first letter, which is E and then looking at the last letter to see whether the type is a perceiving or judging type, in this case (ENTJ) is a judging type so you look at the letter T. ENTJ's primary function is Extroverted Thinking.
From that you can figure out the primary type of all Extroverted types, all you do is get the first letter and find what the second letter is by looking at the last letter. eg ESFP: ES, ENFP: EN, ESFJ, EF etc.
The tricky part is figuring out the primary function for introverts (actually very easy once you understand it) to find the primary function of an introverted type you have to look at the last letter, and that actually points to what the primary function is not, instead of what it is. For example INTP's primary function is Introverted Thinking, this was found by looking at the last letter (P) and that in this case tells you that the primary function is actually Judging so you use the judging letter (T).
So in summary: the last letter of an extroverted type points to what what the second letter of the primary function is, while the last letter of an introverted type points to what the second letter of the primary function is not.
I have recently learnt this and it explains allot but also raises a few questions, but to keep this post brief i'll just finish it here.