Here's why:

* Acids are defined by their ability to donate protons (H+) in solution. While many acids contain hydrogen, it's not the sole determining factor.

* Many compounds containing hydrogen do not donate protons in water and are not acidic. For example, methane (CH4) contains hydrogen but is not an acid.

* The presence of a highly electronegative atom (like oxygen or chlorine) bonded to hydrogen is crucial for an acid to form. The electronegative atom pulls electron density away from the hydrogen, making it more likely to dissociate as a proton.

Examples:

* Hydrochloric acid (HCl): Contains hydrogen and is an acid.

* Methanol (CH3OH): Contains hydrogen but is not an acid.

In summary: While many acids contain hydrogen, the presence of hydrogen alone does not guarantee that a compound will be acidic when dissolved in water.