Short screws

[fubar]

If you want to fasten something with a screw or nail, how far should they go into the underlying material?
I've heard that 2/3 of the nail's or screw's length should go into the wall, or whatever it is you're fastening into, could that be correct?

In the deck we ordered with the house, it looks as follows: first, the screws go through approximately 4.5 cm of wood (in railings) then screwed in a little more than a centimeter.
Do I need to add that the railings are fairly loose? - But according to the house supplier's instructions, that's what is stated.

The entrance, which is similar, is fastened with 4-5" nails, it holds like a rock!

 

[fubar]

One more picture

 

[fubar]

Builder: What do you think about the screw marked deck versus the nail marked entrance?

The material behind is more than sufficient for the length +2. The force will be like when someone leans against a railing.

 

[fubar]

Because a deck railing is a matter of safety, the screw is too short. It can't be said more simply.

Thank you! -no further questions.