结婚未必一定幸福。

Jiéhūn wèibì yídìng xìngfú.

Getting married doesn’t necessarily mean you’ll be happy.

做得好未必能得到回报。

Zuò dé hǎo wèibì néng dédào huíbào.

Doing well doesn't necessarily guarantee a reward.

天气预报未必准确。

Tiānqì yùbào wèibì zhǔnquè.

Weather forecasts may not be accurate.