ものだ: general principles and expected behavior
Read ものだ presenting a general characteristic or behavioral norm rather than a single event. Distinguish the force of advice or prohibition and the recollective たものだ.
Saying what generally happens
人は失敗から学ぶものです。 says that people learn from failure as a general principle. It does not report what one specific person learned from one particular failure.
Plain forms such as a dictionary-form verb connect to this expression. 時間がたつと記憶は薄れるものです。 describes memories tending to fade over time without assigning every memory a fixed rate of change.
Behavior presented as a norm
人の話は最後まで聞くものです。 can teach that one should hear people out. It presents desirable behavior as expected rather than simply giving statistics about what people actually do.
人の失敗を笑うものではありません。 normatively says one should not laugh at others' failures. This is a judgment against that behavior, not a lack of ability to laugh.
Scope of generalization and recollection
A generalization using ものだ can still be the speaker's view or a social standard. Consider what kind of claim it is rather than treating it as an exceptionless scientific law about everyone.
子どものころは川で遊んだものです。 recalls repeated childhood experiences. Distinguish a general characteristic in 遊ぶものです from past recollection in 遊んだものです through verb form and context.
Quick check: Does 約束は守るものです。 report that a promise was just fulfilled?
Show the answer and why
No. It presents keeping promises as a general standard of behavior. It does not establish whether a particular promise was kept.