Life and decisions can change

Maybe im the odd one out, and nothing against those whose opinion differs from mine but just a little curious to the thought process surrounding life choices/ideals that are agreed upon before marriage/long term relationship that one person may end up changing their minds about later on and how does that make them unfair or a bad person?

The amount of posts on here where the husband or wife (but from most ive read its mostly the husband) who spoken to there significant other about important life decisions like the amount of kids you might want to have, or wanting to eventually get married, or anything thats a major life choice and then later on gone on to change their minds or no longer want that and have sooo many woman commenting about how they are wrong/unfair and essentially had 'lied' to their partner is confusing to me. People change their minds all the time and life does not always go the way you hope/plan. You cant both say "yes we both definitely want 5 kids" and then a few years down the track after only have 1 or 2 kids and being financially/emotionally/mentally/physically struggling and one of you deciding you actually dont want 5 kids - how does that make that partner a bad person?

Sorry ive just seen so many posts/comments like this and i feel like its such a weird vibe on here sometimes lol