Infancy
Often, if a baby has superpowers, they will randomly activate. Sometimes it can overlap with other reasons (e.g. they're angry, sneezing, etc.) but other times, it's just random. Reason for this is probably a combination of inexperience and lack of mental ability to control powers. Often, super-babies
can use their powers on purpose but often do it by accident as well.
If a person has only recently developed or begun using their powers, they will often have trouble using them. Sometimes, they can't activate them at all but more often they can think, "I am going to use my powers now" and do
something with their powers, but not what they want. Sometimes, they can activate their powers but not
deactivate them, automatically stop using their powers when they don't want to,
fly but flounder about like a bird that can't fly right,
lift things with their mind but not control where the object goes,
teleport but can't control where they end up, activate a different power from the one they wanted to, or create too much of something (someone with
fire powers creating too much fire for instance). Inexperienced people are also common to random, involuntary power activation, especially as a response to emotions or physiological responses/sensations.
Emotions
Sometimes, a character's powers will be rendered uncontrollable with emotions, particularly negative emotions, and
extra common with anger and fear/worry. These people might either not be able to use their powers correctly when they have these emotions (or too much of these emotions, for example being
too angry/scared), the powers will have side effects with these emotions, they will involuntarily activate when the character has these emotions, or sometimes these emotions might even make the character turn evil if they try to use the powers while feeling them. The fix is either trying not to feel the emotions, trying to control the powers in
spite of the emotions, or even another emotion—most commonly a positive one, usually "love" (whether romantic, platonic, or just love in general, sometimes they use the
word "love" when it actually seems more like optimism), hope, or just happiness. Anger is more likely to cause problems with powers if the character is expressing their anger through shouting, gritting their teeth, growling or anything involving movements of the body.
Non-expressive anger or characters who are grumpy in a "disciplined" way are less likely to be unable to control their powers, although there are exceptions.
Puberty
Sometimes, characters will get uncontrollable powers around puberty. This can be either because of hormones, or because the powers
have only just arrived or have become more powerful (thus overlapping with inexperience). This often applies to whole species.
Physiological things
Such as sneezing, coughing, hiccuping, burping,
farting, etc. Either the powers will activate when one or a combination of these happens or if something like that happens while the character is using their powers, it will have side effects.
The trope for this is
Malfunction Malady. The physiological response thing mentioned above can also happen if sneezing and/or coughing is a symptom, so it can be hard to tell if it's the actual illness/allergy that's causing the power incontinence or the sneezing/coughing, but other times it's more clear. Sometimes, the sick/injured/allergic character will try to use their powers but nothing will happen, the wrong thing will happen, or the powers will be "weak" compared to the character's usual powers. Sometimes, their powers will become uncontrollable even if they're not coughing or sneezing or will be replaced with different powers.
The powers are "running out"
Sometimes, powers deplete with age or need to "recharge". If the character is on the verge of outgrowing their powers or will need to recharge them soon, they normally won't have random power surges but will often use the powers less reliably, gracefully and/or efficiently.
