하지만 is used mostly in writing so when used in speech, it sounds insistent/sharp. In Jaewoo Kim's examples, 그런데 comes across as 'unlike the ground's expected to get wet' or 'although it rained'. I figure it's because 그런데 originaly roots from '그러하다', which means 'to be like that'. 그러하 + ㄴ데 = 그러한데 ⇒ 그런데 ⇒ 근데. It rained, but unlike it's expected to get wet, the ground didn't get wet. When you speak, I'd suggest you use just 근데.

근데 is short form of 그런데 Anyway 그런데,하지만 both are very similar in usage They are both used when you contrast what you've just mentioned A little difference is that 하지만 totally shows the reverse against what you've said like the one above, 그런데 rather narrates actions like having a connection with the first action but showing reverse too. Ex) 비가 왔다. 하지만 땅이 젖어있지 않았다. it'd rained but suprisingly the ground wasn't wet.. 비가 왔다. 그런데 땅이 젖어있지 않았다. it'd rained then I found that the ground wasn't wet 그는 착하다, 하지만(그런데) 그녀는 나쁘다. > it has no connection between two actions just showing opposite It's pretty difficult to say the difference :P hope you get to find it. however you can use both in the same situation, just get the basic meanings of them.