Image quality reduced when opened.

I don't know how to explain it properly, but recently if I download a picture and open it in Photoshop is appears rough and edgy. For example, I just recently downloaded this.

However, when I attempt to open it using Photoshop is appears like this. (I couldn't open the screenie in Photoshop as the quality was reduced even further)

I just started using Photoshop recently, but when I first started using Photoshop it didn't do this. It happens, I now know, with any image. Even those that were never downloaded such as the screenie I provided have a drastic decrease. If anybody got provide an explanation as to what I'm doing wrong and tell me how to fix it I would be thankful.

I notice that you are viewing the image in Photoshop at 66.7% magnification.

To get a true representation of the image you should view it at 100%.

I feel like a complete fool right now, but thanks!