No problem. Lightning is pretty ingenious. A "channel" is simply a multisig bitcoin UTXO shared between you and your channel partner. When you open a channel from your own Lightning node to another node, part of that UTXO balance is controlled by you, and the other part is controlled by your channel partner. Every time a transaction is made using that channel, the relative balances are updated to reflect who controls what. The protocol is designed so that only you can spend your portion, and your channel partner can only spend their portion, and at any point either one of you can decide to "close" the channel which will send your balance to your bitcoin wallet, and the channel partner's balance to their wallet, minus any on chain transaction fees. These channels (UTXOs) are linked together by the lightning protocol to facilitate payments from the originating node to the receiving node. When you use a custodial lightning wallet, you simply have an account with whoever runs that node, and your "balance" in your custodial wallet is not actually anything you possess but rather (if they're honest and trustworthy) part of one of the channels on their node.
Discussion
Cool. Thanks.
So back to my question.
If I run my own LN node and I receive a million times 21 sats from different people with their own nodes and channels, would I be able to close those channels in an economically viable way?
And how about if 90% of the people that zapped me use a custodial solution? That would probably be much less channels to close for me, right? Because most of them will use Strike or WoS.
The sender wouldn't matter from the perspective of your node. They could be custodial or not. As long as their payment can find a route through the network of channels between the sending node to your receiving node, then you will receive it into one of your channels.
For the sake of simplicity for this example, let's imagine your node has only a single channel with a total capacity of 30M sats, and let's imagine it's a brand new channel that your channel partner opened to your node. This means all of the balance would be on your channel partner's side; they own the entire balance of the channel until you receive a payment. Let's say you receive a payment of 1M sats from someone. The relative balances of your channel would automatically update, and at this point if you closed the channel you would receive a single UTXO to your bitcoin wallet of your 1M sats and your channel partner would get a single UTXO of 29M sats, minus fees to settle the transaction on chain.
But instead of closing, you leave the channel open and begin to receive thousands of little lightning payments of varying sizes, with most of them being zaps of 21 sats. Each time you receive one, your relative balances with your channel partner updates on your nodes, and over time you let them accumulate until you've received a sum total of 21M sats into. Now at this point you own 21M sats of the channel, and your partner owns 9M. If at this point you decide to close the channel, you would still receive only one UTXO of your 21M sats, and your channel partner one UTXO of their 9M, minus fees. In this way, self custodial lightning can be a great way to consolidate smaller payments and DCAs into larger UTXOs.