In yogic philosophy, Ahimsa means non-harming. Seems simple enough, don't do any harm. Most basic moral laws of the land suggest we follow this code. But, in reality this goal is very difficult to maintain. It is a goal that must always be worked towards, even though we can not get there in absolute.
I screw up just about every day. Some days I screw up more than others. I try though I really do. Often I do well. I say the right thing, do the right thing, make the right decision. But, no matter how I try, I can't be perfect. Some days I can't even be half-decent. Other days I'm a real screw up. Such is life. No being in a body is perfect, and there is nothing that can be done to make us perfect. We are all naturally flawed by our interactions.
We would be better if we spend our time being mindful of what it is that we impact. Instead we adhere to a list of predetermined "do's and don't do's". We, as a society have accepted that if we adhere to this list, we have obligated our requirement to "not harm", but we do harm anyway. The key is to examine our actions to avoid harming unnecessarily. What is necessary harming? It is the actions we must do to sustain life in its very basic form. In order to grow a garden, we must uproot the weeds, shoo away the bugs, rabbits, and deer. We must cut trees to let in the sun and make fence posts, and till the soil, killing millions upon millions of sentient ground bugs. From this view you can see that creating a garden is quite disruptive, even violent.
You may drive a new hybrid, because you want to use less gas and fight global warming, but with research, you may find that is was more carbon reducing to keep the old car running a few more years than to order the factories to make you a new one. You may be a devout vegetarian, because you do not want to harm animals, but you may find that the tofu you're eating is made in factories on the coast in Asia, and the briny discharge from these tofu plants is killing the bays and coastlines. We see ads telling us that we should buy new eco-friendly clothes, isn't it more "eco-friendly" to wear the ones we have even though they're stained? Is it eco-friendly to buy anything we don't need?
As we look deeper into non-harming we begin to see that no absolute rule of thumb to applies to all, in all situations. There is no blanket law book we can follow that will cover everything we do without a second thought. Each and every action we do must be audited by our sense of reason, our sense on non-harming, or wisdom. Every action you do will need a judge, and that judge is you. Only you truly know when you have harmed unnecessarily, only you know when you have truly sinned.
Relax, be gentle with yourself. Non-harming means you too. Take care of yourself, no one else will. Keep yourself strong, so you may help others. If a mosquito bites, kill it. If your dog has flees, kill the flees, not the dog. Do not think only of the results of your actions, but consider more the motivations behind your actions. We need to make thought out decisions about what we buy, eat, and do. Forgive yourself for making an impact. Show gratitude towards those people and things you do impact. Consider each and everything you do. Use your naturally wise judgement to tread as lightly as possible.