Yes sometimes the presence of blood in your stool can be harmless as long as it goes away after a day or two.
If you continue to have blood in your stools after a few days then you should go see a doctor about it because having blood in the stool that lasts longer than a few days is certainly not normal.
The blood in the stool could be caused by anal fissures, hemorrhoids, anal tears and even from straining trying to poop due to hard stools.
Sometimes an anal fissure will heal on it's own but if not see a doctor about it.
Sometimes blood in the stool can indicate a more serious condition such as cancer in more serious cases.