The course of true love never did run smooth.
The following lines (up to line 151) provide a great catalog of all the obstacles writers have used over the centuries to serve the same function as Wall in the play-within-a-play of Act V. Notice, though, that the obstacle between Hermia and Lysander is not listed in the catalog. That obstacle, of course, is simply Egeus's quite arbitrary objection to Lysander, and in the end it amounts to nothing.