In the Clinton birth chart you can see the RED line between Sun and Moon is a square aspect. This stress orientated relationship causes a repeating mistake. The mistake is often a blindside error and is most likely internal rather than caused by an outside event or person. An opposition between compatible planets can actually be not to bad an aspect. For instance Mars and Jupiter are not a bad combination as long as the impulsiveness of Mars does not push Jupiter's luck.
Conscious effort produces better results with oppositions than with squares.
An example is a Mercury opposition to Mars which creates an very argumentative person. If the planets are compatible this is not a problem. If the planets are not compatible this can be every bit as stressful as a square. For instance Mars and Saturn in conjunction is not a great combination. Either Mars or Saturn will debilitate the other depending on the sign and setting the conjunction is in.