why do we expect ALLAH Subhanau Wa Talaa to forgive us?

If we don't forgive each other, why do we expect ALLAH Subhanau Wa Talaa to forgive us?
If we don't show mercy to others, why should we ask ALLAH subhnau Wa Talaa for mercy for ourselves?

This point is highlighted in this beautiful Hadith. "He who is not merciful to people ALLAH Subhanau Wa Talaa will not be merciful to him...'' [Bukhari]