the proof of the pudding is in the eating

Proverb

One can only claim that something is a success after it has been tried out or used.

Japanese Meaning

物事は実際に試してみないと本当の価値や結果が分からないこと / 真価は行動に移してみた時に初めて明らかになるという意味 / 実際にやってみるまで評価できないという教訓を示す表現

We can design all the plans we want, but in the end the proof of the pudding is in the eating when it comes to launching the product.

本当に成功するかどうかは、実際に試してみて初めて分かる。

Sense（1）

One can only claim that something is a success after it has been tried out or used.