Unlike fiat which the amount in your bank account remains what it is, bitcoin in your wallet will constantly fluctuate, meaning that there is chances that you can gain or lose your bitcoin.
You don't lose bitcoin due to price fall 1
BTC = 1
BTC.
When the price of bitcoin pumps, the fiat equivalent is what you see as profit but the bitcoin remains same. You only lose your bitcoin if you sell at lost or you are scammed or hacked and your bitcoin transfered from your wallet. Anything besides this, you are not losing your bitcoin, just hold and the price will appreciate again.
Also, the money in your bank does not remain what it is, it losses value every day while bitcoin doesn't lose any value.