Even if your words are not true, you can still encourage others. It is vital to consider the context in which such encouragement will be given.
Telling someone they’re strong to encourage them to lift a heavy item is not always unethical. It could also be a good way to get their attention and motivate them to do so. It could cause problems if someone is physically incapable of lifting an object and being told they are strong can put them at risk or harm them. If this is the case, then it’s better to get someone to lift that object for you, than to impose an identity on someone who can’t.
Similarly, it may not be wrong to encourage a fellow student by saying they will succeed on an exam. This could boost the person’s confidence. If the individual is struggling to understand the material or needs extra support, this could pose a problem. If this is the case, you should offer advice and assistance rather than assigning a person a name. They may lack necessary knowledge or skills to be successful on their own.
It is important to consider the context in which your actions and words are being used.