In these and similar spoken uses, can is perfectly acceptable. Nevertheless, in more formal usage the distinction between can and may still has many adherents. The increased formality of may sometimes highlights the role of the speaker in giving permission. You may leave the room when you're finished implies that permission is given by the speaker. You can leave the room when you're finished implies that permission is part of a rule or policy rather than a decision on the part of the speaker.
Bone spurs can be very painful.
You may see him at the concert. From the mountaintop you can see the ocean on a clear day. Even an experienced driver can get lost in this town. 6 More at auxiliary and primary verbs and may . Both cannot but and can but are standard expressions that have been in use for hundreds of years.