"If at first you don't succeed, try, try again" we were told as children. This was designed to prevent discouragement. Discouragement saps our strength and will. Knowing that difficult goals take time, effort and experience does help us understand what to do when we fall short of goals we have set. Goals can be unrealistic or we may need to develop more skills or more persistence.
Here is a goal that does not seem possible to attain in a lifetime: "Love the LORD your God with all your heart, with all your soul, with all your mind, and with all your strength" (Mark 12:30). This goal is the greatest and requires us to try and try again. The fullness of that goal may not be within our grasp as humans, but we can reach a higher level. Aim high. Shoot for the moon and you may make it to the clouds.