I really should have been more careful.

Meaning

Taking responsibility and acknowledging lack of care.

Examples

• John: 'I'm sorry, I made a silly mistake.'
• Alice: '<b>I really should have been more careful.</b> I'll be more attentive next time.'
• John: '<b>I really should have been more careful.</b> I should have proofread it again.'
• Alice: 'I made a careless error.'