Just to add this good explanation...

So if you focus on a specific point, objects closer than that point will blur as they get closer, and similarly objects further away will blur as distance increases.

The range of distances over which you have acceptable focus is known as 'Depth of Field' (or DoF) and it's affected by two factors: 1.> How far away you are focusing (the further away you focus, the larger the DoF) and 2.> The size of the aperture (e.g. iris or a gap in your fingers) through which you're looking (the smaller the aperture, the larger the DoF - this is for the reasons explained by u/waitforthestopsign)

The DoF is not symmetrical - in fact objects closer to you than the focal point quickly blur (but we tend not to notice because these objects are often in our peripheral vision); objects further away than the focal point blur more slowly as distance increases.

A consequence of this is that in very bright light the iris in our eyes contracts to limit the amount of light entering the eye, which has the effect of increasing the DoF and makes it much easier for the lens to focus - this is because it the lens doesn't need to be as accurate, and deficiencies in the lens (e.g. long-sightedness) become less noticeable. The effect is particularly noticeable on objects that are close to us which is one reason why reading in good light can be so much easier that in poor light.