Many have divided men into Body and Soul/Spirit, but I don't think that's accurate enough. Men can be divided into two parts: Rational and Irrational.
Our rational side comprises not only our body but our logical/rational thinking. Rational is anything that can be explained rationally (never mind the redundancy). Overall, it's our rational side which helps us to survive. To be efficient, you must be rational.
However, we have an irrational side, related to feelings. This is what makes us truly humans, and not just robots with a particular purpose. It's thanks to irrationality that we have creativity/innovation; however, that's the only good thing about it. It's due to our irrational side that we have fears, insecurities, depression, etc.
The problem is that our irrational side cannot be explained. It is part of human nature not knowing what we really are (and it's also part of human nature to want to find an answer). You can't convince your irrational side with arguments and force it to not feel sad; apparently, it just happens.