Choosing alts above BTC was the best choice ever, did put in about 6 projects in the beginning, 4 of them made from 2-3x in first 3 months.
Another thing that should be addressed is the ability to look on market and understand when to get in and when to reap few X from your investments and not be too late, that's the hardest part I think.
You were just lucky because this March all altcoins made at least 15x in short period of time. Nobody lost money, everybody won. But the market does not always grow. Sometimes the trend turn to bearish and stuck it for ~2 years.
If you don't take your profit and sell your coins you will lose your money day by day in bearish trend.