When I was 19 in 1989 I sold my 65 Topps Joe Namath RC and 55 Topps Sandy Koufax RC to put a downpayment on my first house. Bought the house for $69,000, sold it 4 years later for $120,000...so the cards did well! (House is worth about $600K now, on the beach on Puget Sound)
I then at the time sold a 1984 Donruss set to buys some furniture, lol.
Recently a couple of months ago I set broke a 1957 Topps set, got twice as much as expected (super high grade set) and paid for the adoption of our latest daughter (I have 4 daughters, 1 son,
). Wife was pretty happy about that....had enough left over for a nice leather sectional to replace the old couch.
I am not much of a seller, don't like it, but through my life I have a lot of examples where cards were very key and helped with a lot of important things. One of the many reasons I have such a passion!