I think the sentence you are talking about, the better translation should be "To learn without thinking, one will be lost in his learning. To think without learning, one will be imperilled."
To learn without thinking means one is very unlikely to apply such knowledge, thus will feel very lost in his learning. Because one does not know what he/she is learning anyway. And by thinking, one can learn more related things as well.
To think without learning is more dangerous. Let me give an example. If you think that as long as you buy a stock, you will earn, than you are in danger of losing your savings because you never learn what are the mechanics behind that allow one to earn when he/she buy stocks. That is thinking without learning.
Hope it helps! Cheers!