“A repost is someone spending their reputation to extend your reach.
A like is someone spending one second of their time to pat you on the head.
A zap is someone spending hard money to incentivize you to continue spending your time to provide value in a similar manner.”
Source:
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The beauty of it is too is that it can be for something as simple as making someone laugh, or being civil, whatever. The ability to send even just a single sat is still spreading that value.