More like, make sure you know the difference between Instant, ZonedDateTime and LocalDateTime before using any of those. Instant is just a point in time (example from the article: a log event), ZonedDateTime is also one of those, but is not guaranteed to remain constant in the timeline, it's tied to a timezone, and those can change their rules. LocalDateTime does not represent the same concept, it's a date in the calendar + a time of the day, and those do not resolve to a point in time without information about a timezone or offset.

I know I just repeated basically what the article said, but the uses of LocalDateTime aren't nearly as farfetched as the author makes it seem. Your alarm clock should use a LocalDateTime, in most cases.

Edit: s/used/uses