According to Midrash the pasuk uses the singular tense, “VaYikchu ish machtaso…” in describing the actions of Nadav and Avihu because “lo natlu eitzeh zeh m’zeh,” they did not consult with each other. As a result, they erred and were punished. This seems a bit difficult to understand. It's clear from the Midrash that each one of the Bnei Aharon independently reached the same conclusion and acted of his own volition (though see Netziv 10:1). Wouldn’t their consulting with each other only reinforce their mistaken belief? Apparently not. Though they may have each initially reached the same conclusion, the process of opening their thinking to critique, even (or perhaps especially) to a sympathetic listener, would afford the opportunity to reflect further and realize the error.
This critique of Nadav and Avihu shows the importance of peer review. "Aseh lecha rav u'knei lecha chaveir," we read in Avos. One of the meforshim explains that the Mishna uses the term "knei," to acquire [even if it costs money], when speaking of a friend and not when speaking about a Rav because the input of a peer is even more valuable than that of a Rav and should be pursued at all costs. We are social creatures. Our avodas Hashem flourishes when undertaken in collaboration, not by dint of individual effort alone.