A mobile wallet doesn’t have data for the entire blockchain, so how can you confirm that a transfer really made it into a block?
Proof of reserves at exchanges also uses Merkle trees: the platform publishes a root hash, and each user can verify whether their balance was included using their own Merkle path.
A Bitcoin block header is only 80 bytes long, and it contains the Merkle root for all the transactions in the block.
Back when I didn’t understand this, I wasted enough money to buy milk tea for several months.
If you don’t understand something, don’t go in with a large position. It’s safer to try with a small amount first.
$BTC 83105.85 (+0.96%)

This is just my personal opinion and should not be taken as a basis for buying or selling.