It is the heart (soul) we must understand to find out why we suffer or have joy in our lives. The following is from the Ofudesaki, the most sacred scripture in the world

Everyone, what comes from the innermost heart, if one truly

quickly understands it, if this matter happens…. 7-27

Interpretation:

What comes from our heart is our fate. Our hearts collect our negative actions as debits (negative energy) and eventually releases it as negative fate. We must understand this concept, so we can eventually prevent sufferings and obstacles in our future.