If Bitcoin can be compared to cash transactions, the Lightning Network is analogous to an online system of decentralized credit: traders exchange IOUs, keep running tabs on their expenses, and only use the blockchain when their interaction concludes. That’s a big difference from the sign-and-send procedure for an ordinary, on-chain transaction. More to the point, the Lightning Network requires active involvement from all involved. Each party needs to be online at the same time; you can’t just post a QR code on your website to ask for tips. A successful Lightning transaction requires choosing an optimal payment path from among thousands of intermediaries, and—since nodes are constantly flickering on and off—that path needs to be recalculated each time.