Greek banks are about the most emotional trade in the stock market right now. The problem for investors is that there are few real reasons to buy or sell—everything depends upon what political game the new government wants to play.

Another strong rebound in bank stocks Thursday after days of hefty falls shows there is still a price at which investors will jump back in. Conciliatory words from the new deputy prime minister on Wednesday evening about excessive zeal in comments from inexperienced ministers also helped.