Slow but sure wins the race

This refers to the fable of the hare and the tortoise. The race was won by the slow tortoise, which plodded steadily on while the fast hare, confident of victory, took things too easily.

See also:

• Constant dripping wears away the stone
• If at first you don't succeed, try, try, try again
• It's dogged that does it
• Little by little and bit by bit
• Little strokes fell great oaks
• Rome was not built in a day
• Where there's a will there's a way