A misconception which some people may have, is that Force can be represented in a complete way as a number. But in reality, Force is a vector, just like Velocity is a vector, and Speed would be the magnitude, of a Velocity vector.
There could be numerous individual forces acting on a body that has mass. Because they are all vectors, they could be pointing in different or opposing directions, and could even cancel out. But, a vector-summation of all the individual forces acting on a body, will result in the Net Force.
So, a rather dreamy perception that people might have could be:
“There are numerous forces acting on me, and yet I don’t seem to be moving. I’m just sitting in my comfy-chair, with gravity acting on me – Yet I could remain stationary.” Or, ‘My arm could be engaging a wall, with force, and not moving. How is any of this possible?’
Well, if a Scientist computes the vector-sum of all the individual forces acting on a body with known Mass, thus computing the Net Force, then the body will Accelerate with certainty, as a function of this Net Force, and of its own Mass. As long as the Net Force is not a null vector, the result is unconditional.
And of course Velocity is the integral of Acceleration, so that as long as this effect is only short-term, its integral over a longer period of time could be approximately null. Position is the integral of Velocity, and we could still find, that in spite of all the forces I interact with, I haven’t left a certain room for hours.
As to whether the body deforms or not, with these forces acting on it, was something I wrote about in the above posting, but is also something which differs for fundamental particles, from how it is with elastic bodies, that are composed of many fundamental particles.
And, If a Scientist knows that additional forces could be acting on a body, but in a way that cancels out, or in a way understood to be negligible, he also doesn’t need to include those in his computation of the Net Force.