Picture a wild horse standing in your backyard. It is not running away. What is preventing you from riding it?
My class answered: catch it, make it your friend, a saddle, experience. Under all of those is one word, harness: the straps around the head, the saddle on the back. A horse could take people ten or twenty times faster than walking, but only the harnessed one was safe to ride. That word is what this field now calls the work of making an agent safe to use. The agent is the horse.
To see why, separate three kinds of programs that people mix up.
Ordinary software is deterministic: same input, same output, every time. It runs code line by line, top to bottom. When it gets stuck, it stops with an error message, which programmers call an exception. It never decides to try something else.
A chatbot is a large language model you talk to. It came out a few years ago and everybody was amazed. It knows everything, but it cannot do anything. It cannot open your files or send an email. The chat window on a company website is a chatbot, not an agent.
An agent is that same model with arms and legs. You connect it to tools: a browser it can drive through Playwright, the tool testers use, plus a database and an email server. The connection is usually MCP, the model context protocol, or an API, which are standard ways for one program to talk to another. Then you give it a goal, not steps, and it works in a loop. It tries, fails, reads the goal again, finds the root cause, and comes back with a better strategy, until the goal is reached or an exit condition is met.
Two programs need the same file, and the file is missing. The first one stops and prints an error. The second one searches your whole disk, finds the file in a folder you forgot about, and finishes the job. Which one do you want running on your laptop overnight?
Neither. Not until you decide what the second one is allowed to touch. The first one wastes your night. The second one finished the job, and to find one file it opened every folder you own: your photos, your tax returns, the file where you keep your passwords. Searching was never the problem. Searching with no limit on what it may touch is the problem, because the same loop that found the file could just as easily have moved or deleted whatever stood in its way. That is the wild horse: all the capability, and nobody holding the reins.