The tip section of the thumb governs the intuition or "Gut Instinct". The second phalanx (middle section) shows the development of the logical mind. Compare the two sections to see which is crossed by deep horizontal lines, or "Blocks". In most cases, one phalanx will have two or three distinct blocks, while the other remains relatively clear.
The phalanx which contains these blocks reflects the aspect in which one is likely to develop a blind spot, missing some important detail.
If the middle section on your thumb has several horizontal lines, your logic often cannot be trusted. Whenever there is a conflict between what you think and what you feel, your intuition is the more accurate. If the first phalanx shows these blocks, the reverse is true - trust your logic.
You can also look to see if several vertical lines cross one of the phalanges, which indicates that the "blind spot" has been overcome.