It is definitely hard singing live and idols are always tired from being overworked and all. Sometimes it's best not to strain their vocals! Still, it can be pretty humorous or even o_O when you catch an idol lip-syncing! In some cases, it could be that they're not used to lip-syncing and the event called for it, so they had no choice.
For others, you can argue that they were just singing with a back track and wasn't lip syncing the whole time. Either way, they made a mistake and their mistakes are cute, so check out these instances below!
IOI's Kim Se Jung
At very beginning
Red Velvet's Yeri