The mind can play tricks on us. It can make people see things and hear things that aren't there. It can cause pregnancy symptoms in people who aren't pregnant. It can cause people to have seizures, be blind or paralysed with no physical cause.
The placebo effect is so well recognised (the belief that taking a medication will result in improvement in physical or mental health symptoms is so strong it creates an improvement) that a placebo group is always included in clinical trials of new medications.
The mind can create experiences so intense and real that your physical body changes so yes, it can make you believe that you've seen/heard something that didn't happen. Particularly if your belief is based on a psychological 'need' to believe it.
So if you think someone you know who is dead and you loved (or even if someone told you X lived in your house and died) and is communicating with you, you want to believe that and you do. So when you 'ask' for signs you get them. Your concious mind is invested in that, your subconscious mind creates it for you. For millenia there has been a belief that people who can see/communicate with spirits are special. They used to hold high positions in society and still do in many cultures so add in 'specialness' and that increases desire to believe.
People who believe that a drug is making them better often get better. If you tell people half way through a medical trial that they're receiving placebo, their improvement in symptoms drops even if they're being given the real drug.
In our culture we've believed in ghosts for so many centuries that it's ingrained and therefore will always be considered by some people as an option in explaining things.
If some of the posters here came along and said ' I believe I'm possessed by a demon or cursed by a witch because this happened' we'd say no. We'd say you misinterpreted it or whatever. Because our culture left belief in demonic possession and witchcraft behind a long time ago. But some of the experiences listed here would have been seen as proof of such in the past.
But it's still very much alive in others. And we condemn it. When we hear about people being beaten to remove spirits or children ostracised or even murdered because they communicated with spirits, electrical devices malfunctioned in their presence witnesses by others, people saw ghosts or heard noises or got ill because of them or whatever nonsense we say ' bollocks, evil spirits, possession or witches don't exist'.
Our culture thought numerous people in the past were witches, demons, vampires or werewolves. We think it ridiculous now. But we still hold on to a little belief in the possibility of ghosts so it's offered as an explanation with no evidence.
In time that'll change.