The discovery of oil comes with a huge blessings capable of transforming individual lives communities, states and even countries if well managed. But a situation where the proceeds are miss managed it will turn to be a cause as individual will rise against individual, states Wil rise against starts, countries will rise against countries.
The answer is in both ways, it could be a blessing and it could be a curse, it depends on the leadership of the country. You can imagine Nigeria blessed with crude oil and other mineral resources that can't be finished still retarding in progress. But there are many countries without crude oil and hardly have mineral resources to sell but still found their ways around it and are doing better than Nigeria. This is where creativity and leadership come in. Good things in the hands of bad people will never be allowed to show their goodness.
Practically, if a good country is blessed with crude oil, it should use the proceeds to harness the potential of other aspects of the economy and invest also in the people. But the reverse is the case in African countries, for example, they just relax and become reliant almost solely on crude oil since it is free money for them. Imagine countries having an income source of over 85% crude oil, some are even worse than that. What will they do when the crude oil is finished or the fight against carbon emission is finally won and petroleum fades off? These are countries blessed with good lands for agriculture, but laziness, corruption and lack of vision for the future have entrapped them.