For great results, finish cooking pasta in the sauce, adding a little pasta water.
In a large saucepan, heat oil and garlic over medium until fragrant. Add onion, celery, and carrot and cook, stirring occasionally, until vegetables are soft. Add beef and cook until just cooked through, 8 minutes. Season with salt and pepper. Add tomatoes and bring to a boil. Reduce to a rapid simmer and cook until slightly thickened, 10 minutes. Season with salt and pepper. Serve with 3/4 pound cooked pasta.