The exasperating thing about AWS is that it inevitably turns engineering teams into equities and derivative traders. Yes, all programming is about balancing storage, CPU, memory, network I/O against each other, but AWS introduces the complexity of needing to reason about these things over time horizons that are long by a startup's standard.

If all of your business's metrics are sharply up and to the right, you probably don't need to worry so much, but if your goal is operational cost efficiency for a relatively stable workload, AWS is a challenge. That may be a blessing in disguise, as self hosting becomes a reasonable thing to consider if your needs are nontrivial and relatively inelastic.