l understand that if you are long an option and it goes up in value because you're +ve delta and vega, with every point underlying goes up the option will go up in value by the delta amount, all else being equal, and if the volatility increases 1% the option will go up in value by it's vega amount x1, all else being equal, so the option will be worth more in those favourable delta and vega movements so when we sell the option, it will be worth more, and we profit. question is if we're already short the option, so -ve delta and -ve vega and underlying goes up, why isn't this beneficial from an option valuation perspective based on the -ve delta and -ve vega, since with every underlying point goes up the option will decrease in value by the delta amount, all else being equal, and if the volatility increases 1 % the option will decrease in value by it's vega amount x1, all else being equal, so the option will be worth less, making a closing trade profitable? am l missing something here?

Implied volatility and delta as well as the other greeks are not absolute values. Options prices can move at a smaller amount than what you expect and vice versa. I am mainly, an options buyer and most will tell you to be an options seller. The reason being you will get a high winning rate of say 90%. Of course, there are no free lunches, with that very high win rate, you will get very low amount in premiums collected. In addition, both options buyers and sellers have to deal with slippage courtesy of the market makers. If they see you are desperate to get out, they will move prices far away to cause you huge losses. That we have no control over. In most cases, waiting to sell or buy your options to close your position the very next day works in your favor 90% of the time.

Yes, you are missing something. The thing you are missing is called “gamma.” An option’s p&l wrt gamma =0.5*gamma*dS^2

Yeah your missing the fact, which you already stated earlier actually, that if vol goes up so does the price of the option. Which you have to buy back to close the position.

one of the difficulties in orienting oneself with an option is you don't know the delta at a point just by checking the change in price at a point. you only know a condition relating the second derivative to the flux through the boundary. i would add if you were to move volatility to infinity all delta would be +/-0.5 i.e. every strike is at the money. the curvature of the vol surface in time and the curvature by delta are anything but random. most experts say at the money is 3 factor, smile is then separate pointwise, probably a cubic spleen.

on a serious not though i know what you are saying it is one of the problems. you can change the sign of the delta delta without changing the sign of the vega if you have more than 1 option so you are changing to the foreign currency and the martingale 'drift' is now (2sigma-r) not r but all else is the same. the problem arises quickly due to the fact that any asset is also a riskless bond to measure others. if you have a usdjpy combo and this happens you need to say stop i am now a japanese and consider the option call a put priced in yen with a positive yen balance to hedge but vega and gamma remain the same otherwise the so called vector space hoax fails. non uniquness for an mgf from the point of view of the unit disk is a disaster. my message to experts is have another look at markov processes and i think you'll find there's something called a gamma process which has an mgf with very different coeffiicients to your own. otherwise i fear your risk adjusted returns are heading very rapidly towards a very dark place

If you are an option newbie like me, you overthink the problem. If you are long a call options, when the underlying goes up (positive delta), the option is worth more, you make money, when volatility increases (positive vega), the option is worth more, you make money. If you are short a call options, when the underlying goes up the options is worth more, you lose money because you have to buy it back at a higher price. In your brokerage account, your broker put a negative sign in a short call (a liability), so you start off with a negative amount, it is more negative if the underlying goes up (higher liability, negative delta). Same with volatility (higher liability, negative vega). I don't know if I make any sense to you, or anyone else?

Yup, you’re right. I don’t know why people are even telling him about gamma waves or martingale drift, when the problem is simple as that.

Gamma waves, martingale drift, those are professional option traders' explanation of what we amateurs call buy high sell low and sell high buy low.

Surely, but then again, no point making things more complicated than they appear when the answer is in the basics..