When it comes to their own net worth, millennials sure are an optimistic bunch. According to a survey by TD Ameritrade, more than half of the generation thinks they’ll be millionaires one day.

One-fifth of millennials think they’ll amass that wealth by the time they’re 40.

One-fifth of them think they’ll amass that wealth by the time they’re 40, and most expect that their earnings will come from a job they’re happy with in their chosen trade.

Not to rain on their parade, but the financial reality for most millennials looks much more modest.

As noted in a story by The Economist contrasting the two, the Brookings Institution recently conducted an economic study that found that millennials are less wealthy than people their age were in any year from 1989 to 2007.

The economy may be looking up, but the crash of 2008 has narrowed the opportunities for young people to make millions.

“This is a financially optimistic group that’s feeling positive about the economy, the job market and their own plans. However, they will need to develop saving and investing habits that will help them reach some pretty big goals,” said TD Ameritrade Chief Strategist JJ Kinahan.

While 70 percent of millennials reported that they were actively working on saving money, retirement wasn’t the most common fund.

Forty-three percent claimed they were saving for a vacation, and 39 percent said they were building an emergency fund account. Twenty-five percent are saving for their children’s education.

In other ways, though, millennials are more conservative than their elders.

The Brookings study notes that millennials are buying houses, getting married, and having children later than any generation before them.

While they’ll live longer than previous generations, they’ll have a harder time amassing the wealth to retire.  

Bottom line: Despite the power of positive thinking, life probably won’t be all yachts and first-class vacations for most millennials — and almost certainly not in their 30s.