If you want to avoid forgetting your cryptocurrency coins then you can use some portfolio application for cryptocurrency. Blockfolio is one of the most well known cryptocurrency portfolio tracker and you can use that to monitor your cryptocurrencies and to help you to see the prices and other small details regarding to the cryptocurrency that you have invested in.
I have also been using blockfolio for a while now and I can really testify to what you have said, this app is really very good in keeping record of ones holding and giving live update on them. One good think I also like about blockfolio is that, you can get some tokens that are not even listed in coinmarketcap on it and will point one to the direction where the coins are being trader.
Even with all these solutions blockfolio has brought, it still may not completely solve the problem, as the only problem is not just forgetting the token or coin entirely, but also forgetting the access details to where the coin is being held. I have an exodus wallet right now, where I have 10% of my coins and I cannot remember the details and not able to even recover it.