Capitalism is based, mainly, in 2 principles: private property of the means of production and free market.
Both tend, inevitably, to oligopoly and monopoly (since, when improving their competitiveness, companies will eventualy succed over the rest, who won't be able to compete any more, and leave the market to the most succesfull ones, which in their new status won't be affordable rivals for new small companies). Think, for example, in a company who success in lowering their pricess (maintaining quality) to a point where is not viable for the others to lower theirs without losses, and therefore can't compete anymore, being his market share absorbed by the succeding one, which then grows again, being able to again get more income, invest in new products or more efficient means of production, lowering prices again, etc. If one or few can still compete, new initiatives won't have the means and resources to challenge the already well stablished giants with competitive pricess, and innovative companies/products can only gain traction/market temporarily, getting into the same "tend to oligopoly/monopoly" loop again.
Once oligopoly/monopoly is reach, companies can control chains of production/producers and distribution, which can also turn into abussive policies, abussive prices and lobbying against consumers/citizens interests. BTW, this is exactly what we are living nowadays in most "developed" countries, with a bunch of big companies controling sectors such as food, clothing, tech, chemistry, transport, etc. through dozens of other subsidiary companies. In my country, we've seen an extraordinary hike in food prices fueled only by stellar profits from the main supermarket chains (this is: companies rising their prices not due to increased production costs, but to rise their profit margins so their investors have more and more benefits. And this is happening in almost every developed country now!).
So yeah, it's perfectly fine to be angry about a biased by birth system (and we haven't even considered things like exploitation, workers/consumers rights, environmental damages, rampant inequality, lack of access to basic services such as education or health, underpaid people who have to get 2 or 3 works just to pay rent and food, and so many other undesired stuff of both a total free market capitalism or a regulated one, which is what we have now!).
P.D.: For those who say that in capitalism you can get enough money or even get rich with enough effort, just think/research about how many hard working people can't afford basic stuff (housing, health, education, supplies, food, etc.) despite having full time jobs, even effort-intensive jobs. And remember that there's not enouth room for everyone to be an entrepeneur, since we live in a limited world with limited resources and when one owns something, others aren't allow to use that resource for their own initiatives.