There may have many reasons-which is related to their character,experiences,dreams,hopes,or for their Beloveds or even out of happiness..it is not a weakness,but a strength especially when we cry/feel sorrow for others.

Only deep hurts can make one cry............!!

Crying occurs for innumerable reasons.When in joy crying occurs.Likewise pepole tend to cry when there're undesired things seen happening.Anger also causes crying which's mostly shrill.So controlling anger helps reduce shrii-crying.

Due to failure ...

Crying has no special relationship with sorrow. Tears come when u r overcome with feelings... and that need not necessarily be sorrow. But mediocre people seldom experience any emotion in life other than sorrow. So they link it to sorrow.

Crying is an exocrine process. ''that is, a process in which a substance comes out of the body. Other exocrine processes, like exhaling, urinating, defecating and sweating, release toxic substances from the body. There's every reason to think crying does the same, releasing chemicals that the body produces in response to stress.'' So, it helps to relieve stress by ridding the body of potentially harmful stress-induced chemicals. So, it is a biological role of emotional stress.

Sadness, failuire, physical pain etc

In both cases
but for me will cry for simple things and when something serious will not be able to cry