Because learning a second language (L2) is difficult, many learners start with easy words that look like their native language (L1) to jumpstart their vocabulary. However, this approach may not be the most effective strategy in the long-term, compared to introducing difficult L2 vocabulary early on. We examined how L1 similarity affects pattern learning in L2 by teaching English monolinguals either an Englishlike or Non-Englishlike artificial language that contained repeated patterns. We found that the first words that individuals learned in an L2 influenced which words they acquired next. Specifically, learning a new word in one session made it easier to acquire a similar word in the next session. L2-similarity interacted with L1-similarity, so that words that looked more like English were easier to learn at first, but they were less effective at influencing later word learning. This demonstrates that although native language similarity has a beneficial effect early on, it may hinder long-term learning by decreasing recognition of repeated patterns within a second language. This surprising finding demonstrates that making early learning easier may not be the most effective long-term strategy. Learning difficult vocabulary teaches the learner what makes the new language unique, and this general language knowledge about language structure is more valuable than the words themselves. We suggest that difficulties during learning are not always to be avoided, as additional effort early on can pay later dividends.