An experienced engineer who built 12+ AI agent systems explains why current autonomous agent hype is mathematically flawed. Error rates compound exponentially in multi-step workflows (95% per step = 36% success over 20 steps), token costs scale quadratically making conversational agents economically unsustainable, and tool engineering for AI interfaces requires specialized design. Successful production agents work within bounded contexts with human oversight, focusing on AI handling complexity while traditional engineering ensures reliability.