Many things can cause a grown man to cry, as emotions are not limited by gender. Crying is a natural and normal human emotional response to certain situations or stimuli. A grown man may cry in response to a wide range of emotions,when the person is sad or that person is feeling lonely. 

When he/she lost someone or a grown man may cry in response to a special moment of joy, such as the birth of a child. 

Crying is a natural way of expressing emotion,we cannot say a grown man is weak.

There are many things that can evoke strong emotions and cause someone to cry, including:

Heartfelt moments: A touching scene, such as a wedding, birth of a child, or reunion with a loved one, can bring someone to tears.

Grief and loss: The death of a loved one or the loss of something dear can be deeply painful and evoke a strong emotional response, including tears.

Overwhelming emotions: Strong feelings of sadness, frustration, anger, or guilt can all lead to crying.

Acts of kindness or heroism: Seeing someone perform an act of selflessness or bravery can be deeply moving and inspire tears.

Memories: Revisiting memories from the past, either through photographs or videos, can evoke strong emotions and bring someone to tears.

It's important to remember that crying is a natural and healthy way to express emotions, and that it's okay to cry regardless of age, gender, or cultural background. Crying can be a cathartic release and a way to process and heal from difficult experiences or emotions.