While doing some training I inadvertently smacked the lens of my night vision against a hard object, totally my fault and totally damn near ruined my NVD. Luckily I had in place a Sacrificial Window over the objective lens of the NVD. Sacrificial windows aren't cheap, the run between $25.00 and $35.00 bucks depending on where you find them. That being said, $25 to $35 is nothing in comparison to a decent set of NVDs. When I purchased mine they went right at $4000.00.
When you are training and training correctly, equipment will get damaged, your physical body will get beat up, mentally you will be challenged. This is what we want, we want to push ourselves in training, we want to learn our limitation, limitations on our equipment as well as better understand what our mental and physical capabilities are as we begin to move up and to the "over The Hill" points in our life.
Just because we train hard doesn't mean we are abusing our equipment for the sake of abuse. Using appropriate and often times included equipment designed to help safeguard equipment and your body- should be used. I see a lot of people running equipment sans the protective equipment. This sometimes is because they observed someone else doing it and believe they should in-turn emulate that person or they are not using the protective equipment out of ignorance. Ignorance in both forms of uniformed ignorance and tacticool, "i'm doing this because it looks cool" ignorance.
Use protective equipment when it's available, if you feel it will hinder you yet you haven't actually attempted to try it, you are just speaking from a position of ignorance.
Here are some pictures of a $30 dollar protective lens saving my $4000 set of NVDs from severe damage.