I am realizing, in this era of AI, for IT sector scope, time, cost are not real constraints, with software, tools and techniques, forecasting is better possible. For a project manager, the real constraint is resource/s all above constraints are dependent now a day, more on resources than any other factor, which is unlike before. In majority cases I have observed that your project cross limits of scope time cost, when you have issue/s with resource/s and not with process (scope) or schedule (time) and the allotted funds/reserves. In civil projects, still situation is far better. Most resources are required to implement the concept/design. Being sole owner; PM is all time buried under scope, time and cost constraints but resource is still secondary constraint.
In IT situation is different. Mostly in all cases project manager is well aware of scope-time-cost. They keep sponsor/s or the client well in loop about changing situation/s, put queries or doubts whatever they may have/had. In other words, for a PM at core scope time cost is not a high constraint, but it is constraint for higher management. Mostly it is sponsor!
What I am observing in IT or KPOs is, the real constraint is shifting from scope, time and cost to resource. verified resource>domain expert resource>subject matter expert or required software, tools and techniques expertise is becoming scarce day by day.