The market hasn't been kind to Citigroup (NYSE:C) this week; it's down 1.14% so far on this last day of trading. We can thank Bank of America (NYSE:BAC) for that, and the herd mentality that led to a market panic after the superbank missed earnings expectations.

Big-bank roundup
Here's where Citi's peers and the rest of the market stand on this last day of trading:

  • B of A is down the most: 4.04% so far.
  • JPMorgan Chase (NYSE:JPM) is down big, as well: 2.68%.
  • Wells Fargo (NYSE:WFC), down just 0.60%, is have the best week out of the big four banks.

Foolish bottom line
Citi, like its peers, was having a fine week until Wednesday. B of A reported first-quarter earnings, missed analyst expectations by $0.02, and investors lost their minds -- sending B of A, Citi, and the rest of market down into the same pessimistic abyss.

And this after Citi reported impressive first-quarter earnings only two days earlier:

  • Net income rose 30%.
  • Total revenue rose 3% year over year, no small feat when even sector stalwarts like JPMorgan and Wells Fargo saw revenue declines: 3.8% and 1.4%, respectively. Even better, Citi's revenue rose 12% from the fourth quarter.
  • Net losses at Citi Holdings, Citigroup's "bad bank," dropped by 21%.

For Citi investors, the good news is CEO Michael Corbat's superbank is up 0.29% already on the day. The rest of the big four look to be in recovery mode as well. There's a lesson to be learned, here, one that Foolish investors learned a long time ago.

On a day-to-day, week-to-week, and even month-to-month basis, the stock market can be capricious. One minute your favorite stock is up, the next, it's down, either for seemingly no reason at all, or maybe because herd mentality has taken over, and investors are doing what everyone else is doing: taking counsel of their fears.

But Fools know to stay focused on company fundamentals and the long term, and to stay in their stocks for as long as they believe in them. "Get rich slowly." Perhaps my favorite Foolish investing motto, and one to keep in my during weeks like this. 

Fool contributor John Grgurich owns shares of Citigroup and JPMorgan Chase. Follow John's dispatches from the bleeding heart of capitalism on Twitter @TMFGrgurich.

The Motley Fool recommends Wells Fargo. The Motley Fool owns shares of Bank of America, Citigroup, JPMorgan Chase, and Wells Fargo. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a lovely disclosure policy.