Great works are performed by perseverance.

(product development) project

difficult / hard, probably impossible

a year

project (planned endeavour)

three years; the third year / (education) the third school year / (figuratively) a long period of time, several years

three years; triennial / three years old

the above / the top (position or direction) / the surface of / superior in skill, age, level, etc.

in addition; furthermore / on top of (which)

success / success in life, achievement in the world