当然、其实、终于、才2、才3、就4

Inside a sentence, 当然 just means 'naturally, no surprise'. As a one-word answer, it reads like 'obviously, dummy' — fine with close friends, risky with your boss. Natives soften it: 当然可以, 当然没问题, 当然啦. English 'of course' covers both jobs, so learners never feel the drop in temperature. In-sentence it stays neutral: “看着这，老北京们心里当然不舒服。” ── 《这还是茶馆儿吗？》

“看着这，老北京们心里当然不舒服。” (Seeing this, old-time Beijingers naturally feel uncomfortable about it.) ── 《这还是茶馆儿吗？》

其实 means 'actually, here's the truth' and it exists to fix a wrong idea. Put it in front of the subject when the whole picture is wrong: 其实我不太想去. Put it right after the subject when one person is the surprise: 他其实早就知道了. After the verb it breaks — 我说其实 sounds like a translation glitch. And it never means 'right now'; that job is 现在.

终于 is emotional: something you waited and suffered for finally happens. 最后 is flat: it marks the last step or last item in a plan or story. So the late train earns 车终于来了, while your weekend recap earns 最后我们去了三里屯. Swap them and one sentence sounds underwhelmed, the other sounds wrong. 终于 usually drags 了 with it — that 了 stamps the wait as over: 终于下班了.

才 on a number means the number came out smaller than you expected: 他才三岁, 才三十块钱, 才五分钟就好了. English flips between 'only', 'just' and 'barely', but the Chinese job never changes. 只 states a flat limit with zero opinion: 我只有十块钱. So when you are shocked or sympathetic, 才 is the one; when you are just counting, 只 is enough. Saying 他是三岁 for 'he is three' is simply broken.

Stick 就 after a time word and that time picks up an attitude: 他六点就起来了 sounds impressed, or maybe annoyed, but never neutral. Swap in 才 and the meaning flips hard — 他八点才下班 is 'he does not get off until eight', a complaint. Same clock, opposite feelings. 早就 pushes it further into 'ages ago': 我早就知道了.