I meet loads of people who have collected coins everywhere. They have 20 different types of wallets with a little bit of value. It's due to happen that people will loose their private keys or forget that they even have an account. Over time that value could accumulate pretty big. What will happen to these 'lost' coins? Will these stay on the Blockchain forever, accessible to no one anymore?
A coin or token stays where it is unless someone or something transfers it to another location or wallet. So in this case, if a user forgets or lost his private key, then the coins or tokens inside that wallet will stay in it forever. This is the effect of decentralization (not saying its is a negative effect not a positive one). Having those coins or tokens be lost then we could consider them as burnt. Thus, contributing to the scarcity of that specific coin or token and, a possible, increase in its market value.