The Little Loop in Its Head
An Agent doesn't get everything done in one breath—it goes one small step at a time, and at each step asks itself three things:
想（Think）：现在该干嘛？
做（Act）：调用某个工具（搜索 / 查数据库 / 算一下）
看（Observe）：拿到结果，离目标更近了吗？
→ 没完成就回到“想”，再来一轮A More Realistic Example
Goal: "Tell me how many orders our app got yesterday." An Agent might go around a few loops like this:
想：要拿昨天数据，得查数据库
做：调用 query_db("select count(*) ... where day='昨天'")
看：返回 1287
想：够了，可以回答
交付：昨天下单 1287 笔Why Loop Around Instead of Saying It All at Once?
Because it doesn't know the result in advance. Before querying the database, it doesn't know whether it's 1287 or 0; before searching, it doesn't know what it'll find. It has to do a step and see the result before it can decide the next one—just like you check your balance before you know whether you can still place the order.
自测 · 学完检查一下
想真正动手做题、记进度、攒连胜？到互动课里练。
An Agent's core loop is "think → act → ___ → think again."
答案：observe
Think → act → observe; if the goal isn't reached, go around again.
In the "check yesterday's order count" example, which loop step does "calling query_db(...)" belong to?
答案：Act
Calling a tool to execute is the "Act" step.
And which loop step does "returns 1287" belong to?
答案：Observe
Taking in the result the tool gives and judging how close you are to the goal is "Observe."
Judge: an Agent always finishes the job in one go and doesn't need several loops.
答案：False
Quite the opposite—it often goes around several times: do a step, observe the result, then decide the next. This lets it handle tasks that take multiple steps and depend on intermediate results.
Why does an Agent loop instead of outputting the whole answer at once?
答案：Because it has to see the tool's returned result before deciding the next step
The result is unknown, so it must "do a step, look at a step"—the loop exists for exactly this.
This "think → act → observe" loop has a common name in the field: ___ (fill in the English).
答案：ReAct
ReAct = Reason (think) + Act (do), where Observe (look) is an implicit part of the loop. It's fine if you can't recall the term—just remember "the loop."