Tricky uses of "dao"
You probably learned the result complement -到 a long time ago, as part of words like 看到 ("to see") and 听到 ("to hear"). But other times it's less clear what the -到 really means. Like the difference between 买 and 买到 or 做 and 做到. What -到 adds is a clearer message that something has really been achieved.
The Difference a -到 Makes
Adding -到 after a verb makes it very clear that the desired result was achieved. If you looked and you saw, then 到 indicates that. On the other hand, not adding 到 makes it unclear whether or not the desired result was achieved. It can have the effect of making a verb mean "try to verb." So 做 without -到 is kind of like "try to do," but when you want to make it very clear that results were achieved or must be achieved, that's when you want to add -到.
Let's look at another example. The difference between 找 and 找到 is that 找 means "to search" (in other words, "to try to find"), whereas 找到 means "to find," that the search was successful, and results were achieved. So if one were to say "你一定要找," it would mean "you must try to find it" and "你一定要找到" means "you must find it."
做 vs. 做到
It's often assumed that if you're going to 做 something, it'll be to completion. But if there's ever any doubt, or a situation where "to completion" needs to be made crystal clear, use 做到.
- 我 还 没有 做。I haven‘t done it.
- 我 下 个 星期 可以 做。I can do it next week.
- 我 相信 你 一定 能 做到。I believe you will be able to do it.
买 vs. 买到
买 is another one where success is normally assumed, but every now and then it's not so easy to just buy something. That's where 买到 comes in handy.
- 我 还 没有 买 。I haven't bought it yet.
- 我 没 买到 。I wasn't able to buy it.
- 这里 买 不 到 进口 食品 。You can't buy imported good here.
学 vs. 学到
You know how when you're studying, you know information is going into your brain, but you're not sure how well it's really sticking? Well, when you're sure of what's stuck, you can use 学到.
- 我 想 学 中文 。I want to study Chinese.
- 我们 今天 学 了 很 多 生词 。Today we studied many new words.
- 在 这个 公司 工作 ，我 学到 了 很 多 东西。Working for this company, I learned a lot of things.
拿 vs. 拿到
A simple act of physically picking something up or taking something usually involves 拿. When the object becomes some kind of hard-to-get document, however, 拿到 is useful.
- 你 拿 小包 ，我 拿 大包 。You take the small bag, I'll take the big bag.
- 不 知道 什么 时候 能 拿到 我 的 工作 签证 。I'm not sure when I'll be able to get my work visa.
- 如果 他 拿 不 到 绿卡 ，我 就 跟 他 分手 。If he can't get a green card, I will break up with him.
想 vs. 想到
If you think of 想 as "looking for ideas," then 想 and 想到 are very similar to 找 and 找到. One difference, though, is that 没想到 means "never imagined." It's not that you tried to think of something and failed, it's just that the idea never occurred to you.
- 一定 要 想 一 个办法 。You have to think of a way.
- 你 想到 了 什么 好 办法 ？Have you thought of anything good yet?
- 我们 都 没 想到 他 这么 生气 。None of us imagined that he would be so mad.
追 vs. 追到
This one is tricky, because "pursue" is a metaphor, and there's no obvious result. "Catch" sounds way too misogynistic and old-fashioned. 追到 actually involves more than just effort on the part of the pursuer; you have to move the girl's (or guy's) heart.
- 怎么 追 女孩子 ？How do you pursue a girl?
- 那 个 女孩子 ，你 追到了吗 ？ That girl, did you win her over yet?
- 如果 你 追到 她 了 ，我 就 请 你 喝酒 。If you can really win her over, I'll treat you to drinks.
了解 vs. 了解到
了解 indicates some kind of deep understanding, often one that only comes over a long period of time. But if you suddenly get some new in-depth information, 了解到 may be appropriate.
- 我 不 太 了解 这个 人 。I don't really know this person well.
- 我们 刚刚 了解 到 一些 新 的 消息 。We just acquired some new information.
- 从 他 那里 ，我 了解 到 了 真相 。I learned the real truth of the matter from him.
联系 vs. 联系到
You can think of 联系 as "initiate contact" and 联系到 as "establish contact."
- 我们 怎么 联系 ？How do we get in contact?
- 你 知道 他 的 联系 方式 吗 ？Do you have his contact information?
- 我 想 跟 你 联系 ，但是 一直 联系 不 到 你 。I wanted to get in touch with you, but could never reach you.