it's not difficult to understand
no es difícil de entender (no es dificil de entender)
"You can learn to cook, it's not rocket science."
"Puedes aprender a cocinar, no es difícil de entender." (puedes aprender a cocinar, **no es dificil de entender**.)
Trust what I am saying; believe me.
to improve an existing product or idea
to forget past mistakes and start fresh
to be responsible for something yourself
Involving serious risk or significant consequences.
to keep something and not give it away