Risk Management is How Adults Manage Projects - Tim Lister (IBM)
It can't be stated too often - either manage risk, or risk will manage you. Projects without risk management are late and over budget before they start. All project work is uncertain. Uncertainties are either reducible or irreducible. Reducible uncertainties can have specific actions to reduce to risks that result from the uncertainties. Irreducible uncertainties can have no specific actions, but must have margin to protect from the resulting risk.
Here's a paper describing how to manage an IT project with Risk Management.
... and as always - you can't manage risk, without making estimates of the probability of occurrence, probability of the impact from the risk, and for the irreducible uncertainties, the statistical processes driving the naturally occurring variance and the needed cost, schedule, and technical margin to protect to project's success from the uncertainties.
So if you're not using Risk Management and associated estimates, you're not managing the project as a adult.