There is still plenty of irrationality in the market, and some startups still burn huge piles of money in search of growth. But as these companies mature, they seem to be discovering the benefits of financial discipline. Uber lost only $108 million in the first quarter of 2021 — a change partially attributable to the sale of its autonomous driving unit, and a vast improvement, believe it or not, over the same quarter last year, when it lost $3 billion. aBoth Uber and Lyft have pledged to become profitable on an adjusted basis this year. Lime, Bird’s main electric scooter competitor, turned its first quarterly profit last year, and Bird — which recently filed to go public through an SPAC at a $2.3 billion valuation — has projected better economics in the years ahead.