"Tu" (the Hebrew abbreviation of 15th) in the month of Shvat was set (Hillel's opinion generally overrules Shammai's) as the beginning of the tithable year for tree fruit: Calculating the tithe on fruit starts again for fruit that sets after that date.
Here is the quintessential Jewish question: How do we emulate God? We are told that we were created by God. We are told that we have a divine spark within us.
We who have become cynical,
Whom life has raised its tough first
Of despair and
Disappointment and heartache
We who have learned to protect our souls
And toughen our hearts
To avoid more anguish